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New Petaluma machine fights mosquitoes, helps environment

Strapped into the cockpit of an apparatus appearing part tank, part lawnmower, part Dr. Seuss contraption, Mechanical Technician William Crain fired up the 3,000-pound machine and drove directly into the marshy waters of the Ellis Creek wetlands in Petaluma.

With paddle-equipped treads, the amphibious vehicle began churning through the water on its way to a stand of bulrush — a haunt for disease-spreading mosquito larvae and a pesky impediment to the flow of treated wastewater from the nearby Ellis Creek Water Recycling Facility.

Up against the Truxor 5000’s whirring, saw-toothed cutter, the fibrous foes never stood a chance.

“We’re still learning it’s abilities and limitations, but so far we are happy,” said Matt Pierce, the operations supervisor at Ellis Creek.

Petaluma city staff this week showed off their latest weapon against the mosquito-friendly plants that have threatened to clog up the wetlands of Ellis Creek — a Sweden-made amphibious weed harvester designed to travel diverse terrain to clear vegetation on land or in water.

The $115,000 contraption was the result of a years-long search for a way to effectively manage the growth of bulrush and coontail in the 214 acres of ponds and wetlands around the facility, plants that have thrived to the point of – in at least one instance – a walkable blanket of vegetation, Pierce said.

The city settled on mechanical removal after ruling out chemical, manual and controlled burn methods, but saw how contractors using a boat-based harvester struggled to remove plants in shallow areas.

“We needed something that could operate regardless of water level,” Pierce said, noting that boat-based designs employed by various contractors over the years would get bogged-down under weight in lower water levels.

Traditionally, Petaluma has resorted to labor-intensive manual cutting of plants along the water’s edge, costing more than $80,000 since 2013. Mosquito abatement costs another $80,000 annually, according to information from the city.

The harvester will help offset those expenses, though Mayor David Glass said during the demonstration on Monday that the ability to maintain the wetlands as designed was more than a matter of cost. The wetlands are an integral part of the operation of the Ellis Creek wastewater plant, providing an extra layer of treatment to discharged water before it winds its way to the Petaluma River.

“We’re in the process of bringing it into full capacity,” he said of the treatment plant, which is undergoing a $15 million expansion that will allow the treatment of nutrient-rich byproducts from food and beverage manufacturing.

Excess growth in the wetlands can impede the flow of water, and decomposing vegetation can reduce the level of dissolved oxygen in the habitat, according to information from the city. The growth also complicates mosquito abatement in an area where monitors discovered West Nile virus twice in the past two years.